A smile is a surprisingly poor guarantee of happiness, because the research shows most smiles are social signals rather than readouts of joy, and some are actively covering the opposite, which is why the truest ones live in the eyes rather than the mouth

We treat a smile as a status report. Someone smiles and we file them under fine, and move on. It is one of the most automatic readings we do of another person, and it is a surprisingly unreliable one. A smile is a poor guarantee of happiness, for two separate…